Abstract
In this study, we show importance of deactivation of the PS II reaction center under drying conditions by comparing desiccation-tolerant Nostoc commune and intolerant Synechocystis sp. PCC6803. N. commune is a terrestrial cyanobacterium distributed widely all over the world. The PS II reaction center and photosynthesis in N. commune were deactivated by dehydration due to sorbitol treatments. In contrast, Synechocystis PCC6803 maintained the PS II reaction center activity when photosynthesis was inhibited by hypertonic treatments. We examined influence of high-light and high-temperature stresses with a PAM method under hypertonic conditions. As a result, high-light and high-temperature tolerances of Synechocystis PCC6803 were decreased by dehydration. While, those of N. commune were increased by dehydration. These results suggest that the remaining PS II reaction center activity, when photosynthesis was deactivated, caused photoinhibition through generation of active oxygen species.
